Interview with Dr. Udo Merker, Heraeus on conductive polymers, what can we expect from polymer capacitors and beyond

 

Last interview of the month with Dr. Schnitter on technological metals moved us to the sphere of passive component materials. Nevertheless the key element mainly for electrolytic capacitors is also type of electrolyte that significantly influences behavior of the capacitors. The fastest growing segment of such materials are organic conductive polymer materials. I have asked Dr. Udo Merker from one of the leading conductive polymer suppliers company Heraeus to answer some questions for EPCI interview. I met Udo first time many years ago and acknowledged his deep conductive polymer knowledge and capacitor experience.” T.Zednicek EPCI

 

>Q1 EPCI: Hello Udo, can you please briefly introduce yourselves, your current position, scope of your work and your experience/relation to the passive components supply chain?

Dr.Merker:

Thank you, Tomas. After my PhD in Physics and a postdoctoral position at the Chemistry Department of Princeton University, I joined the Corporate Research Division of Bayer AG in 1999 to work on the development of electronic materials. Actually, my first project was the development of a capacitor grade tantalum powder for prevention of ignition. From 2002 to 2008, I was responsible for the development of new conductive polymers for electrolytic capacitors in the Central R&D division of H.C. Starck. During that time, I developed conductive polymer dispersions (trade name “Clevios™ K”) that allowed realizing high voltage polymer capacitors for the first time. In 2009, I became the head of the application technology group of H.C. Starck Clevios. After the acquisition of the Clevios conductive polymer business by Heraeus in the end of 2010, I took various positions in the business field of conductive polymers like Head of Innovation, Intellectual Property Manager and Product Manager. Currently, I am managing the technical service for capacitor applications within the conductive polymer group at Heraeus. Our team offers material solutions for the polymer capacitor market to overcome current technical issues and we develop new materials for the next generation of polymer capacitors. We have technical cooperations with all major tantalum and aluminum capacitor manufacturers around the globe. Furthermore, I am in contact with large end-users to anticipate market trends at an early stage.

>Q2 EPCI: Conductive polymers are on the mass market now for about twenty years with constantly increasing its share mainly on aluminum and tantalum capacitors. Can you please briefly summarize the key directions, improvements that this technology has made over the past two decades? 

Dr.Merker:

Reduction of ESR (Equivalent Series Resistance) has been the major driving force for more than 20 years. For a long time, computer motherboards were the dominant market for polymer capacitors: The increasing speed and performance of processors required a growing number of low ESR capacitors with a high ripple current capability. Due to their high electrical conductivity, conductive polymers have reduced the ESR of traditional liquid electrolyte aluminum and manganese tantalum capacitors by about one order of magnitude over the time. Therefore, conductive polymers could replace liquid electrolytes in aluminum and manganese dioxide in tantalum capacitors.

Moreover, miniaturization has been a key for the application of polymer capacitors: The upcoming consumer electronic market had an urgent need for small and low profile passive components. The low ESR of polymer capacitors made it possible to shrink the size and profile of aluminum and tantalum capacitors or to replace multiple of those capacitors with a single polymer capacitor.

Besides these two general technical and market trends, ESR reduction and miniaturization, reliability issues like ignition of tantalum capacitors and leaking of electrolytic aluminum capacitors pushed the usage of polymer capacitors: Ignition of MnO2 tantalum capacitors was an issue around 2000, especially for large case sizes. Polymer tantalum capacitors do not have such risk since conductive polymers do not release oxygen like MnO2 in case of a breakdown. At about the same time, a so-called capacitor plague shocked the aluminum capacitor market.  A high number of electrolytic aluminum capacitors failed in the application at an early stage due to leaking of the electrolyte. Conductive polymers are solid and thus could overcome such leaking issue. Both ignition of tantalum capacitors and leaking of aluminum capacitors promoted polymer capacitors.

>Q3 EPCI: I remember when conductive polymer was introduced to capacitor technologies, it resulted in a lot of mixed feelings. On one side the engineers including myself where fascinated by the “modern organic material”, where mechanical features can be modified independently to electrical features that was not imaginable on the conventional materials such as metals, on the other hand the “unlimited” development potential has resulted in sensitivity of manufacturing process to many new parameters and process control requirements. Can you please describe the latest stage of the technology – can we still count on this material as “unlimited” potential with high chance for further development, or are we in the live stage of mature product that is “understood and used to the maximum of its potential” and in the phase of technology refinement ?

Dr.Merker:

Indeed, the move from liquid electrolytes to conductive polymers involved many new process steps in aluminum capacitor manufacturing. On the other hand, tantalum capacitor manufacturers are more used to sophisticated processes. Just think about the complicated MnO2 process! However, running a reproducible chemical polymer synthesis in millions of tiny components is always a challenge.

In-situ polymerization, where the conductive polymer is formed from precursors inside the capacitor (in-situ), did a great job during the last 20 years and is still improving. However, when the learning curve gets flat and the electronic market continues to move ahead, there is definitely a need for a next generation of materials.

About 10 years ago, we introduced our Clevios™ K conductive polymer dispersions to the capacitor market. Today, these materials gain momentum in the market. Polymer dispersions can be used similar to a paint. There is no chemical polymerization taken place anymore, just a drying. The dispersion already contains the final conductive polymer. You can imagine that such material facilitates the manufacturing process of tantalum and aluminum capacitors significantly.

What is even more attractive about polymer dispersions is their impact on performance and reliability. Our Clevios™ K dispersions overcome the limitations of current conductive polymer capacitors and allow for low DC leakage and high voltage performance. Moreover, capacitors made with polymer dispersions instead of in-situ polymer show a much higher reliability and can access high temperature applications.

To conclude: Yes, we can still count on the potential of the material. There is a lot to expect in the coming years, just to mention 400V polymer capacitors.

>Q4 EPCI: One of the limitation of conductive polymers has been its sensitivity to humidity, respectively the combination of higher temperature and moisture and also higher sensitivity to thermo-mechanical stress such as DLC issues during reflow component assembly. Nevertheless, more manufactures have recently released conductive polymer capacitors capable to operate in harsh environment such as automotive, industrial or space applications. Can you say this is more a result of process improvement on the side of manufacturers where they learn how to apply/design/age the polymer or is it more related to the base chemistry and composition improvements over all ?

Dr.Merker:

Actually, it is both, process and material improvement. Conductive polymers are hydrophilic. Thus, moisture is an issue in many cases. Swelling or shrinkage of the polymer layer can induce some mechanical stress. Moisture in combination with elevated temperature can degrade the conductivity of the organic polymer. Capacitor makers have done a great job in optimizing their capacitor design to reduce the moisture pick-up and to strengthen the interfaces of the different material layers applied during the capacitor manufacturing.

A major step in this evolution typically requires some new material. For example, despite all efforts, polymer capacitors could not really meet the reliability requirements of automotive and space applications for more than 20 years. The introduction of conductive polymer dispersions has been a game changer here. These new conductive polymer materials boost the reliability of polymer capacitors to a level that allows using them in such harsh environment. Therefore, it is not surprising that conductive polymer capacitors have emerged from consumer market and have entered the high reliability market recently.

>Q5 EPCI: I have focused up to now mainly on electrolytic capacitors, but do you see some new trends in application of conductive polymers to new components – such as supercapacitors, or completely new applications outside of capacitor technologies?

Dr.Merker:

Thank you for this question. Actually, there are many more applications for conductive polymers besides electrolytic capacitors. For example, conductive polymers have been applied as antistatic coating on photographic films and on packaging trays of electronic components for more than 20 years. Even for modern LCD display manufacturing, conductive polymers are used for antistatic. Other applications for conductive polymers, like touch panels, OLED (organic LED), OPV (organic photovoltaic) and printed electronics have emerged in the last years. There is quite some research literature on using conductive polymers to improve some properties of supercapacitors. The future will tell us if there really will be a significant market for conductive polymers in supercapacitors.

>Q6 EPCI: There are some new deposition techniques on the market such as 3D Aerojet printing referring capability to deposit even organic materials in thin layers. Are you investigating some of such methods suitable for conductive polymers and what deposition techniques might be relevant for this type of material, if you can disclose?  

Dr.Merker:

There are many deposition techniques for conductive polymers available like dip coating, spin coating, spray coating, slot-die coating or printing. Printing is one method we have focused on in the last years. We offer conductive polymer products for printing methods like screen printing or ink-jet printing.

3D coating of conductive polymers has not really been requested in the market so far. Most applications require only very thin layers in the submicron range. For electrolytic capacitors, old fashioned dip coating is typically applied. Actually, this is still the easiest and most efficient way to deposit conductive polymers in a porous structure of an electrolytic capacitor. This might change when new capacitor designs will emerge in future.

Thank you Udo for your time and willingness to share your opinions with us.


more about the Heraeus company can be found at the company’s homepage here (www.clevios.com)

for further details about conductive polymers, have a look in a book co-authored by Udo Merker: PEDOT Principles and Applications of an Intrinsically Conductive Polymer.

 

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